Discharge lamp circuit



J. A. NUCKOLLS DI SCHARGE LAMP CIRCUIT v Aug. 1, 1967 v 2 Sheets-Sheet 1 Filed Sept. 4, 1964 g- 1, 1957 J. A. NUCKOLLS DISCHARGE LAMP CIRCUIT 2 Sheets-Sheet 2 Filed Sept. 4, 1964 acid/s, mg.

'OOOQOO fmlz 0/: v 5 Ire 1% 3,334,270 DISCHARGE LAMP CIRCUIT Joe A. Nuckclls, Hendersonville, N.C., assignmto General Electric Company, a corporation-of New York Filed Sept. 4, 1964, Ser. No. 394,498 6 Claims. (Cl. 315-471 I i The present invention .relates to a circuit for starting and operating a high intensity are discharge lamp, and

more particularly concerns a starting and operating circuit for such lamps operated by direct current.

High intensity are lamps of the above type frequently are constituted bylamps containing high pressure xenon gas. Such lamps are normally rated to operate at 100 to 200 amperes, 25 to 35 volts D-C and may well be operated by conventional D-C generators, or batteries, or by a 3 phase step-down transformer and filtered supplier, which may be designed to accommodate a range of lamp wattage levels. The DC supply can be controlled by feedback to provide lamp load regulation and load adjustment. T

drawbacks. -In certain cases, the circuit arrangements were such that the components were not adequately protected from or able to withstand the effects of the high voltages and high currents employed in the startingmechanism of the circuits. In other cases, the circuit arrangements did not have sufiicient reliability in operation, and in still others cumbersome and expensive equipment was required to effect the desired starting and operating functions and in a very inetficient manner.

It is an object of the invention to provide an improved circuit arrangement for starting and operating gas discharge lamps such as high pressure xenon, gas discharge lamps.

It is a particular object of the invention to provide a circuit of the above type which efiiciently and reliably produces high voltage pulses for igniting the gas discharge lamp.

It is a further object of the invention to provide a circuit of the above type which is compact in form,'eco nomical to manufacture, and has long operating life.

Other objects and advantages will become; apparent from the followingdescription and the appended claims.

With the above objects in view, the present invention relates, in a preferred embodiment, to an operating and ig- United States O ignite the lamp, however, a high voltage starting pulse nition, circuit for operating a high pressure gaseous dis charge lamp from a low voltage, high current, unidirectional current source comprising an operating circuit ineluding a current limiting impedance, a decoupling recti fier and the lampconnected in series across the source terminals, and a two-stage pulse generating ignition cir cuit connected across the operating ci rcuit, comprising in its first stage an operating capacitor, a silicon controlled rectifier having a control electrode, and a step-up transformer, the primary of the transformer and the silicon controlled rectifier being connected in series across the operatingcapacitor to form a discharge loop, and avoltage sensitive switch, preferably a glow discharge lamp, having a predetermined breakdown voltage connected betweenthe control electrodeof the silicon controlled rectifier and the operating capacitor for energizing the opcrating circuit when the voltage across the operating capacitor reaches a. predetermined level, and the second stage of the ignition circuit comprising an oscillating circuit connected between the secondary of the step-up transformer and the lamp for inducing high voltage pulses for igniting the lamp.

The invention will be better understood from the following description taken in conjunction with the accompanying drawing in which the single figure illustrates an embodiment of the invention.

As shown in the drawing, the operating circuit for discharge lamp 1 includes a low-voltage direct current source such as a direct current generator 2, conductor 3, ballast resistor 5, decoupling power diode 6, transformer 7, and conductor 8.

Discharge lamp 1 illustrated is a xenon arc discharge lamp comprising an envelope 9, anode 10 and cathode 11. The lamp typically operates from approximately amperes and 34.5 volts D-C. Source 2 can therefor'ebe a 40 volt supply. To ignite xenon lamp 1, a pulse of about 30-60 kv. must be applied across the lamp electrodes to initially ionize the gas.

Connected to the operating circuit, as shown in the drawing, is a starting circuit for the lamp which includes a voltage supply of 120 volts A-C, push starting switch 12,-current limiting resistor 13, and rectifier diode 14. Connected in series across the operating circuit are current limiting resistor 15 and storage capacitor 16. Diode 14 provides half-wave rectification of the AC supply cur rent to .produce approximately a peak voltage buildup across capacitor 16 when starting switch 12 is actuated.

Capacitor 16 thus provides the driving voltage function for a pulse generating circuit 17, shown enclosed in dotted lines, which forms a part of the starting circuit and which develops a high voltage, short duration-pulse across lamp 1. r i I Pulse generating circuit 17 includes current limiting resistor 18 and operating capacitor 19 connected in series between conductors 3 and 8 to forms charging circuit across storage capacitor 16. Operating capacitor 19 provides the required high voltage pulse energy. Gate 200 V is connected through resistance 21 and glow lamp 22, which is typically a neon lamp, to the positive side of capacitor 19 and thus to the anode of siliconcontrolled conductive and will provide a gate pulse and fire silicon controlled rectifier 20. As a' result, the voltage across capacitor 19 is applied across the primary winding of stepup transformer 23, the series connection of operating capacitor 19, silicon controlled rectifier 20 and the primary of transformer 23 thereby forming a discharge loo 1 The secondary of transformer 23 isconnected to one terminal of spark gap 24, the other terminal of the latter is connected to the primary of pulsetransformer 7, and high frequency capacitor, 26 is connected between the latter primary and the junction of spark gap 24 and transformer 23, thus forming a discharge loop with spark gap 24 and the primary of transformer 7. The stepped-up. voltage produced inthe secondary of transformer 23'is applied to capacitor 26 until reaching about 10 toflS kv., it attains the breakdown potential of spark gap 24. The latter gap ionizes and appliesthe stepped-up voltage pulse to the primary of pulse transformer 7. The latter, in turn, transforms this voltage to a magnitude of about $0 to 60 kv., and this voltage is applied to lam'pll which is connected by its anode 10 to the secondary of pulse transformer 7. The lamp gas ionizes and ignites, and when the from DC source 2 still passes through pulse transformer 7 to continue operation of lamp 1. v

Capacitor 16, being connected to ground, is charged by therectified A-C current supply to an intermediate voltage of about 170 volts and will have stored therein approximately 10 joules of energy. This energy serves to maintain the operation of the lamp and develop a hot spot on the lamp cathode until the voltage drop across the lamp falls below the source voltage. Then the source voltage takes over operation of the lamp through ballast resistor and power diode 6.

When the silicon controlled rectifier switch 26 is closed as described, capacitor 119 and the inductance of trans former 23 comprise a resonant circuit providing a relatively efficient energy transfer of 1 joule of energy from capacitor 19 to capacitor 26 in a pulsed manner. Accordingly, it is desirable to match capacitors 19 and 26 to accommodate this energy transfer considering the transfer efliciency. The frequency involved in the first transformation is typically in the neighborhood of 200 c.p.s. Similarly,

when the voltage sensitive switch constituted by spark gap 24 closes, capacitor 26 and the pulse inductance of the enables the anode of the primary of pulse transformer 7 comprise a discharge circuit which transforms, in like manner to the previously described mechanism, the high voltage pulse. The. reson ant frequency of this circuit is in the neighborhood of 1 megacycle.

The discharge of capacitor 19 is buffered from its driving mechanism by the resistance 13. Likewise, the discharge of capacitor 26 is buffered from its driving mechanism by the leakage reactance of transformer 23. The silicon controlled rectifier switch 20 is commutated by the attempted ring-back of the resonant mechanism of capacitor l9 and transformer 23. The provision of thyrector 27 across silicon controlled rectifier 20 ensures that voltage reversal across this rectifier does not exceed its rating. Resistor 21 between glow lamp 22 and gate electrode 20a of the silicon controlled rectifier limits the peak gate current.

While only one neon lamp 22 is shown in the gating circuit, in practice it may be advantageous to provide two or more such lamps in parallel to achieve high reliability. As .Will be evident, silicon controlled rectifier 20 in combination with neon lamp 22, or neon lamp 22 alone, may be considered a voltage sensitive switch which operates through discharge capacitor 19 at a predetermined voltage level. Other forms of voltage sensitive switches,

' such as a semiconductor Shockley diode, may be substituted for the silicon controlled rectifier-neon lamp combination, or merely for the neon lamp, to obtain equivalent results in the described arrangement. As wellknown, glow lamps such as neon lamps, or Shockley diodes, upon reaching breakdown voltage continue to conduct current at a voltage substantially below the breakdown voltage level.

A high frequency by-pass capacitor 28 is preferably arranged in parallel across the operating circuit as shown to ensure that the input to pulse transformer 7 remains at the high frequency A-C ground during the charging of capacitor 26 and during the pulsing of lamp ll, considering lamp distributed capacitance, leakage and other factors. I

The use of a glow lamp in the circuit as described provides a positive gating action for the silicon controlled rectifier, forcing the voltage across the latter to drop rapidly during its heavy conduction period to prevent burn-out of this component. Furthermore, the circuit arrangement is such, as described, as to inherently pro vide pulses on the lamp electrodes which have a polarity corresponding to the electrodes, thus providing optimum starting conditions.

FIGURE 2 shows an alternative circuit arrangement which is similar to that of FIGURE 1 but in which the components and the terminals have polarized so as to provide a common anode connection. This arrangement xenon lamp 1 to be physically connected to ground potential, if so desired. In the FIG- URE '2 arrangement, lamp electrode 10a is the cathode and lamp electrode Ha is the anode.

While the present invention has been described with rcferenceto particular embodiments thereof, it will be understood that numerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as come within the true spirit and scope of the invention. I

What I claim as new and desire to secure by letters Patent of the United States is:

1. An operating and ignition circuit for operating a high pressure gas discharge lamp from a low voltage, high current unidirectional current source, said lamp requiring every high ignition voltage followed by an intermediate voltage greater than that of said source sustained for a time sufficient to assure cathode-warmup in order for the arc drop across the lamp to-fall below the value of the source voltage comprising, in combination, an operating circuit including a current limiting impedance, a decoupling rectifier, and said lamp connected in series across the source terminals, a twostage pulse generating ignition circuit connected across said operating circuit comprising in its first stage an op erating capacitor, voltage sensitive switch means, and a step-up transformer, the primary of said transformer and said voltage sensitive switch means being connected in series across said operating capacitor to form a discharge loop, said voltage sensitive switch means having a predetermined breakdown voltage resulting, in conduction thereof at a substantially lower voltage, a pulsing circuit being formed by the primary of'said transformer, said operating capacitor and said voltage sensitive switch means, said pulse generating ignition circuit comprising in its second stage an oscillating circuit connected between the secondary of said step-up transformer and said lamp for producing high voltage pulses for igniting said lamp, and a storage capacitor .connected across said lamp and said ignition circuit for providing the intermediate voltage for electron emission in said lamp and for charging said operating capacitor.

2. An operating and ignition circuit'for operating a high pressure gas discharge lamp froma low voltage, high current unidirectional current source, said lamp requiring a very high ignition voltage followed by an intermediate voltage greater than that of said source sustained for a time sufficient to assure cathode warmup in order for the arc drop across the'lamp to fall voltage resulting in conduction thereof at a substantially lower voltage and being connected between said control electrode of said silicon controlled rectifier and said operating capacitor for turning on said silicon controlled rectifier when the voltage across said operating capacitor reaches said predetermined breakdown voltage, a pulsing circuit being formed by the primary of said transformer, said operating capacitor and said silicon controlled rectifiensaid pulse generating ignition circuit comprising in its second stage an oscillating circuit connected between the secondary of said step-up transformer igniting said lamp, and a storage capacitor connected across said lamp and said ignition circuit for providing the intermediate voltage for electron emission in said lamp and for charging said operatingcapacitor.

3. A circuit as defined in claim 2, and means for charging said storage capacitor to said intermediate voltage and for initiating operation of said ignition circuit comprising an alternating current source of at least about 120 volts connected across said operating circuit, means for rectifying the alternating current from said source to direct current, and switch means for applying the voltage of the thus. rectified alternating current source to said storage capacitor.

4. A circuit as defined in claim 3, and a thyrector connectcd'across said silicon controlled rectifier;

5. A circuit as defined in claim 3, said voltage sensitive switch means comprising a glow discharge lamp.

6. A circuit as defined in claim 3, said voltage sensitive switch means comprising discharge lamps.

parallclconnected glow 20 Furedy 315-276 X Sims et al 315-201 X Germeshausen 315-464 X Gerlach et al. 3l5-24l McNulty et all 315-476 Mutschlcr 315-476 Nowell 3l5--2A1X Wolfiramm et a1. 315-241 Howell 3l5--24t Pett 315 -24 Nuckolls 315-499 Great Britain. Great Britain.

JOHN w. HUCKERT, Primary Examiner.

R. F. POLISSACK, Assistant Examiner;

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,334 ,270 August 1 1967 Joe A. Nuckolls rror appears in the above numbered pat- It is hereby certified that e Patent should read as ent requiring correction and that the said Letters corrected below.

Column 3, line 23, after "a" insert resonant line 74 after "have" insert been Signed and sealed this 9th day of July 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. AN OPERATING AND IGNITION CIRCUIT FOR OPERATING A HIGH PRESSURE GAS DISCHARGE LAMP FROM A LOW VOLTAGE, HIGH CURRENT UNIDIRECTIONAL CURRENT SOURCE, SAID LAMP REQUIRING A VERY HIGH IGNITION VOLTAGE FOLLOWED BY AN INTERMEDIATE VOLTAGE GREATER THAN THAT OF SAID SOURCE SUSTAINED FOR A TIME SUFFICIENT TO ASSURE CATHODE WARMUP IN ORDER FOR THE ARC DROP ACROSS THE LAMP TO FALL BELOW THE VALUE OF THE SOURCE VOLTAGE COMPRISING, IN COMBINATION, AN OPERATING CIRCUIT INCLUDING A CURRENT LIMITING IMPEDANCE, A DECOUPLING RECTIFIER, AND SAID LAMP CONNECTED IN SERIES ACROSS THE SOURCE TERMINALS, A TWOSTAGE PULSE GENERATING IGNITION CIRCUIT CONNECTED ACROSS SAID OPERATING CIRCUIT COMPRISING IN ITS FIRST STAGE AN OPERATING CAPACITOR, VOLTAGE SENSITIVE SWITCH MEANS, AND A STEP-UP TRANSFORMER, THE PRIMARY OF SAID TRANSFORMER AND SAID VOLTAGE SENSITIVE SWITCH MEANS BEING CONNECTED 